Organic acids find diverse application in polymer, food, pharma and chemical industry. Until now these organic acids are largely obtained through processing of petroleum based feedstocks. Today, there is a growing need across the globe to produce these acids from renewable feedstocks. One of the most significant renewable feedstock available to mankind is agricultural residue that essentially is lignocellulosic biomass. Breakdown of lignocellulosic biomass or other sources of polymeric sugars to simple sugars can be used as a potential raw material to be converted to one or the other organic acids through microbial transformation using one or the other native or improved microorganism.
Fermentation technology for the production of organic acids has been known for centuries (e.g. vinegar and lactic acid). Fermentation of sugars or other substrates to organic acids results in production of acids essentially as dilute solutions. However, almost always the acids are produced as a mixture of acids. Separation and recovery of organic acids from fermentation broths has been a subject of intensive research for more than three decades. There have been several works wherein reactive extraction and reactive distillation have been used for acid separation from fermentation broths. Extractive fermentation has been applied in the production of a variety of carboxylic acids, including propionic acid, as a means of overcoming end-product inhibition. The current economic impact of fermentation chemicals, however, is still limited, in large part because of difficulties of product recovery. Thus, for fermentation products to penetrate the organic chemicals industry, substantial improvements in the existing recovery technology are needed.
Purification processes which have been tried to produce high purity organic acid include multiple recrystallization of calcium salts; solvent extraction using ether or a long chain amine; purification by ion exchange chromatography; electrodialysis; and separation and hydrolysis of organic esters. Although the recrystallization technique can be successfully used to prepare a pure salt, say calcium lactate, the process is expensive and the product must then be acidified with sulfuric acid to prepare the organic acid.
Solvent extraction using ether requires very large volumes of ether. Solvent extraction using solvents like amyl alcohol or a tertiary amine, will lead to the production of impure organic acid containing a mixture of organic acids along with salt and water. The process also leads to the formation of multiple phase and stable emulsions which is difficult to separate into individual components. Further there are also concerns about: (a) removal of entrained and soluble solvent affecting the productivity of the microbe; and (b) removal the important nutrients from the recycled broth. Thus, extraction alone does not economically produce an end product of high enough purity.
In ion exchange technique, as the basicity of the resin increases, the regeneration method must be “powerful” enough to remove the organic acid from the resin. Even selectivity of the resin plays an important role as the resin selected should be selective for the organic acid to be extracted and should not bind the essential nutrients in broth required by the microbes. This will lead to overall increase in the cost for the purification of organic acid.
Electrodialysis has also been proposed for purification of organic acid (Colon, PhD thesis, 1986). One major problem with the electrodialysis process is the fouling and scaling of the membranes, which results from the trapping of certain ions in the membrane's polymer network.
Though some progresses have been made over the past few decades regarding the recovery of organic acids, improvements are needed to meet the requirements for the production of pure organic acid in large volumes.
Reactive separation for the recovery of organic acids by a suitable method has been found to be a promising alternative to the conventional processes. Reactive separation of organic acid from fermentation broth can be done by designing integrated process. Reactive extraction by esterification method can be employed for efficient and scalable strategy for continuous separation of organic acids such as lactic acid, succinic acid, propionic acid and butyric acid from a mixture containing organic acids. It will serve as energy saving, time saving, economical green process.
The present invention defines an integrated process for obtaining organic acid in purified form. The purified products obtained can be used as such or it can be polymerised/derivatized to different forms.